The Late Jurassic sauropod dinosaur, Seismosaurus hallorum, from the Morrison Formation of New Mexico, is reconstructed as a full-scale replica using casts of the holotype. We document the osteology of prepared elements from the thoracic, pelvic and caudal regions in comparison to related diplodocids. The thoracic vertebrae are described pending further preparation. A sauropod femur, collected with this material and believed to have been from the same individual, is also described. Using osteo-morphological comparisons with closely related diplodocids, pre-vious axial length estimates of 39-52 meters for Seismosaurus hallorum are questioned, and the overall length is reinterpreted to have been approximately 33 meters.